1. Background Field
Aspects of the present disclosure generally relate to wireless communication systems, and more specifically, to position determination for mobile stations by facilitating accurate measurement of a round trip time (RTT) using a dedicated network appliance.
2. Relevant Background
Mobile communications networks are offering increasingly sophisticated capabilities associated with position location. New software applications, such as, for example, those related to personal productivity, collaborative communications, social networking, and data acquisition, may use position information to provide new features and services to consumers. Aside from the sizeable commercial potential, regulatory requirements in some jurisdictions may require a network operator to report the location of a mobile station when the mobile station places a call to an emergency service, such as a 911 call in the United States.
Position determination has conventionally been provided using digital cellular positioning techniques, Satellite Positioning Systems (SPS's) and the like. In conventional digital cellular networks, position location capability can also be provided by various time and phase measurement techniques from points with a known location such as access points or base stations. For example, one position determination approach used in CDMA networks is referred to as Advanced Forward Link Trilateration (AFLT). Using AFLT, a mobile station may compute its position from phase measurements of pilot signals transmitted from a plurality of base stations.
Improvements to AFLT have resulted from the hybrid position location techniques, for example, where the mobile station may employ a Satellite Positioning System (SPS) receiver in addition to measurement techniques associated with the reception of base station signals. The SPS receiver provides position information independent of the information derived from the signals transmitted by the base stations. Position accuracy can be improved by combining measurements derived from both SPS and AFLT systems using conventional techniques.
However, conventional position location techniques based upon signals provided by SPS and cellular base stations may encounter difficulties when the mobile station is operating within a building and within urban environments or in situations when high accuracy is desired. In such situations, signal reflection and refraction, multipath, and signal attenuation, and the like can significantly reduce position accuracy, and can slow the “time-to-fix” to unacceptably long time periods. These issues may be overcome using signals from other existing wireless networks, such as, for example, Wi-Fi standards under 802.11x, to derive position information. Conventional position determination techniques used in other existing wireless networks may use round trip time (RTT) measurements derived from signals used within these networks.
RTT measurements from stations (STA) to access points (APs) in short range radio or wireless communication networks, such as 802.11 or Wi-Fi networks, Bluetooth networks, and the like, can be used to determine the location of or localize a station via trilateration. As is understood by those of skill in the art, trilateration is used to determine the intersections of three circular or four spherical areas given the centers and radii of the circles or spheres. Accurate localization can, for example, assist in the efficient allocation of network resources, the provision of location based services, and can provide additional advantages. In conventional networks, APs can be used for localization; however, the use of existing APs has several potential challenges.
It will be understood that, while 2 dimensional positioning requires at least three non-collinear APs, a particular geometry having three non-collinear APs may not be available in an existing deployment. Accurate localization using RTT ranging can require that APs have consistent processing delays with low variance. However, APs with adequate resources for localization may not be available in all deployment scenarios. Further, heavy loading on a given AP such as processing a large memory transfer via direct memory addressing (DMA) may cause variation in the RTT turn-around time and thus degrade localization accuracy and stability. Still further, contention may arise between the localization traffic and the normal data/control traffic if using a deployed AP for localization, leading to delay or loss of localization data. Still further, localization may require configuration or updates to the software/firmware on the AP so as to enable the delivery of network geometry, map URIs or other information. However such configuration and updating may not be possible in all deployment scenarios.
Using RTT measurement techniques to accurately determine position typically involves knowledge of time delays incurred by the wireless signals as they propagate through various devices comprising the network. In practice, when employing conventional RTT positioning techniques, estimating processing delay times may involve extensive additional software at both the STA and the AP to characterize and interpret RTT processing delays, hardware changes in the wireless APs, and time-consuming pre-deployment fingerprinting and calibration of the operational environment.
Accordingly, when using RTT techniques for position determination, it may be desirable to avoid hardware changes in wireless access points or to avoid substantial additional processing so as to improve the position location accuracy and performance in a cost-efficient manner.